(Emitted value instead of an instance of Error) postcss-custom-properties in bulma css

Summary

I'm use Bulma CSS Framework on rails5 app with webpacker. I got warnings like below, When I build css files as ./bin/webpack-dev-server. Does anyone know to eliminate them?

23:37:47 webpacker.1 | WARNING in ./node_modules/css-loader?{"minimize":false}!./node_modules/postcss-loader/lib?{"sourceMap":true}!./node_modules/resolve-url-loader!./node_modules/sass-loader/lib/loader.js?{"sourceMap":true}!./node_modules/import-glob-loader!./app/javascript/stylesheets/application.scss 23:37:47 webpacker.1 | (Emitted value instead of an instance of Error) postcss-custom-properties: /some_rails_app/app/javascript/stylesheets/application.scss:9284:3: Custom property ignored: not scoped to the top-level :root element (.columns.is-variable { ... --columnGap: ... })

Versions

  • Rails: 5.1.4
  • Bulma: 0.6.1
  • Ruby: 2.4.1p111
  • Webpacker: 3.0.2